The invention relates to a device and method for early, inexpensive outpatient evaluation of lung dysfunction, especially lung dysfunction that may be related to PCP pneumonia in HIV positive patients.
PCP pneumonia (pneumocystis carinii pneumonia) is caused by a microscopic organism that grows in the human lungs. It is a serious, opportunistic infection that occurs primarily in immunocompromised persons, and is the most prevalent and most life threatening infection occurring from patients' suffering from AIDS (Acquired Immune Deficiency Syndrome). More than 80 percent of AIDS patients will suffer from PCP pneumonia, and about 60 percent of AIDS patients' experience PCP pneumonia as their first major sign of AIDS. PCP pneumonia is characterized by fever, nonproductive cough and dyspnea on exertion. Chest x-rays may be normal or show a nonspecific pattern of interstitial infiltrates. A gallium scan may be positive but nonspecific. Arterial blood gas may show an abnormally low PO.sub.2 (PO.sub.2 is the partial pressure of oxygen in the arterial blood). The lung diffusion capacity (DL.sub.CO) may be abnormally low, as well as the O.sub.2 saturation measured by pulse oximetry after exercise. AIDS patients or HIV positive patients whose immune systems have been damaged frequently die from PCP pneumonia. Their lives could be lengthened, the quality of their life could be improved, and the expense of their treatment could be greatly reduced by early detection of the onset of PCP pneumonia. PCP pneumonia in AIDS patients often is not diagnosed in hospitals, as hospitalization generally is undesirable for AIDS patients because they are likely to be infected by many diseases that are present in the hospital because of their compromised immune systems.
Although a prior lung diffusion capacity test device is available in some hospitals, it is large and expensive, and rarely is used to diagnose PCP pneumonia in AIDS patients. This test is known as the "lung diffusion capacity measured for carbon monoxide" test, designated herein as the "DL.sub.CO test". There are several known methods of making the DL.sub.CO measurement, which is a strong indicator of a PCP infection within an HIV patient. Despite the potential importance of this test, it is not routinely utilized in most hospitals. This is due to (1) the low capacity of most pulmonary function laboratories, (2) reluctance to contaminate the DL.sub.CO test instruments used by testing AIDS patients, (3) the high cost, (4) the lack of availability of the DL.sub.CO test equipment in emergency rooms, and (5) the inefficiency of sending a patient, especially an AIDS patient, from one clinic to another for testing. It should be appreciated that any time hospital equipment is used in contact with AIDS patients, it must be sterilized before and after use. Such sterilization is time consuming and expensive, and is performed as infrequently as possible.
Historically, AIDS patients have been first diagnosed as having PCP pneumonia when they arrive in a hospital emergency room. In the event such a patient is determined to have PCP pneumonia, the patient is likely to be placed in an intensive care unit for several weeks or more, at a cost of $30,000 to $50,000. Treatment of PCP pneumonia presently is the largest cost component of care of AIDS patients. The death rate of AIDS patients due to PCP pneumonia at this state is approximately 30 percent. If the AIDS patient lives, further treatment costs are very high.
Thus, it is critical that there be an early assessment of the likelihood of a PCP infection in known or suspected HIV positive patients.
It is known that AIDS patients with the longest survival are those in which the occurrence of PCP pneumonia is diagnosed early in the disease progression. A common treatment for PCP pneumonia in AIDS patients is use of BACTRIM or intravenous pentamidine. These drugs are quite toxic, and although they alleviate symptoms of PCP pneumonia, if the patient survives for a long time the toxic side effects can become serious. Early diagnosis of PCP pneumonia would allow less toxic doses of these drugs to be used.
Thus, there is an urgent need for an improved, inexpensive, portable apparatus and associated method for early detection of lung dysfunction, especially in HIV positive patients, and especially to help in early diagnosis of PCP pneumonia in AIDS patients.
Physicians generally realize that excessive amounts of the foregoing drugs often are administered to PCP pneumonia patients. It would be highly desirable for physicians to be able to have an objective basis for better judging the dosages and durations of administering such drugs to PCP pneumonia patients, to reduce the toxic side effects thereof.
There are circumstances in which it is desirable to obtain accurate measurements of the amount of CO contained in exhaled breath of a patient, worker, etc. For example, during pre-natal care it may be desirable to determine if an expectant mother is telling the truth when she states that she has not been smoking. Or, in various industrial working environments, it may be desirable to accurately determine the amount of damage that has been done to the person's lungs by such environment. The fractional uptake of CO subsequently described can indicate the amount of such lung damage.
Accordingly, it would be desirable to have an economical method and apparatus for measuring the amount of CO in a person's exhaled breath.